Materials engineering at the nanometer scale can provide smaller devices than those currently available. In particular, research on semiconductor nanostructures with size-dependent optical and electronic properties, such as quantum-dots, one-dimensional quantum wire transistors and light emitting devices with extremely low power consumption is motivated by potential applications. Carbon is a material of great interest for nanostructures because of its important role in the field of microelectronics.
Carbon nanotubes (CNT) have attracted much attention since their discovery a decade ago (Iijima, Nature. 354, 56, 1991). Due to its high aspect ratio, a CNT can enhance a large electric field. This greatly increases the electron emission in a lower strength electric field. In addition to this, CNTs have a wide range of highly interesting properties and potential applications. Most methods of CNT formation are under the conditions of high temperature (>300° C.) and high vacuum. This type of process substantially increases the cost of industrial production. Although the formations of CNT (Hsin, et al., Adv. Mater. 13. 830, 2001) and carbon nano-onion (CNO) (Sano, et al., Nature. 414, 506, 2001) by arc discharge using graphite electrodes in water under room temperature have been reported, one of the challenging issues is to produce CNTs in high-quality (without any metal catalysts) and large quantity within a short time.